This invention is directed to an apparatus for lifting and towing vehicles. More particularly, the present invention relates to an improved lifting and towing apparatus of the "wheel-lift" variety whereby a vehicle to be towed is supported solely or substantially by its wheels.
In recent years, the design problems confronting those in the towing apparatus industry have become increasingly complex. It is essential not only to design a safe, reliable and cost-effective product, but also to accommodate the increasingly difficult constraints imposed by changes in the design of many modern automobiles. For example, current automotive design emphasizes shock-absorbing bumpers, and a variety of non-metallic or otherwise fragile parts to reduce cost and weight and save fuel. Also, present automobiles employ spoilers, low ground clearance, and small clearances between wheel wells and tires. These features also save weight and reduce drag. However, these same features also present serious difficulties when a modern automobile is disabled and must be towed. Shock-absorbing bumpers, non-metallic parts and spoilers cannot withstand the forces imposed when raising one end of an automobile by a sling attached between the automobile's axle and the boom of a tow truck. Second, the minimal ground clearance available makes engagement of the sling on the axle more difficult and time-consuming. Additional problems with conventional sling-type towing are created by modern, low-clearance parking garages which impede the use of any sling-type towing device which depends upon a boom.
Some of these disadvantages and problems are addressed by wheel-lift towing devices. These devices employ various means to lift a disabled vehicle by its wheels, rather than by the vehicle body structure. See, for example, U.S. Pat. No. 3,897,879, "Vehicle Towing Apparatus", which discloses a tow truck that employs a cradle which, in turn, supports the wheels of the disabled vehicle. The cradle is lifted by a boom attached to the ends of the cradle by slings.
Another type of device intended to overcome some of the disadvantages described above employs a parallel bar and strap system. The system has a beam which is positioned under one end of a vehicle to be towed, and in contact with the tire tread of each of the pair of wheels to be lifted. Then, L-shaped supports are attached to each end of the beam. Each support has a long portion which attaches to the beam and which spans the outside of the towed vehicle wheel. A short portion extends horizontally at a right angle from the long portion, generally parallel to the beam and to the axle of the disabled vehicle, and toward the centerline of the vehicle. The beam and short portion together form parallel members; each pair of members supports a wheel. Each wheel is then strapped to some part of its support to prevent the wheel from rolling out of its support when the towing and towed vehicles accelerate or decelerate. The beam is attached to the towing vehicle by means which allow the beam (and thus one end of the towed vehicle) to be raised and, in some cases, moved closer to the towing vehicle. It is important to decrease this distance, because the weight of the towed vehicle creates a moment about the rear wheels of the towing vehicle. The moment, if large enough, reduces the weight on the front wheels of the towing vehicle and can even lift the wheels. This in turn impedes steering or renders it impossible. It similarly affects braking. Countering this lifting effect requires that weight be added to the towing vehicle forward of its rear wheels, thus adding expense and depressing fuel economy. Shortening the lever arm mitigates this effect.
Currently available wheel-lift towing devices suffer from additional disadvantages. First, the straps can be time-consuming and difficult to use, especially in cold, wet, or other inclement weather conditions. Second, the contact between the parallel members and the wheel is sometimes unsatisfactory because the members contact only a small portion of the tire tread. In fact, some devices only make contact along a line because the L-shaped support is often made of square tubing or pipe. If the tire deflates after the vehicle is lifted, the wheel can drop between the parallel members. On the other hand, if the parallel members are brought closer together to eliminate this danger, the force necessary to roll the wheel out of the support is reduced. Separation of the towed and towing vehicles could occur more easily, causing a serious accident. In either case, the towing apparatus may fail in service.
The close spacing of the parallel members leads to another disadvantage. As the gap between the members decreases, parallel members must engage the lifted wheel farther below the center of the wheel, and well below the lower body line of the vehicle, i.e., an imaginary straight line extending along the vehicle side at the height of the lowest points on the vehicle body. As the distance between this lower body line and the highest point of contact with the lifted wheel increases, the tendency of the vehicle to roll out of the support in the event of acceleration or deceleration is increased.
Fourth, presently available wheel-lift devices generally place the beam and supports on, or very close to the ground before they are connected. Thus, the long portion of the support spanning the outside of the wheel requires several inches clearance. If the outside of the wheel, or any part of it, is in contact with or immediately adjacent to a curb or other obstruction, the wheel-lift device is even more difficult to use or possibly rendered useless.
Fifth, some of the present wheel-lift devices generally require that the centerline of the towing vehicle be colinear, or very nearly so, with the centerline of the towed vehicle.
Sixth, present wheel-lift devices generally require that the wheels of the vehicle to be lifted be turned straight, or very nearly so. If the wheels are turned, the distance between parallel members may be too great to provide adequate contact with both sides of the wheel.
Seventh, many present wheel-lift devices are severely hampered or rendered useless by uneven road surfaces, parking garage ramps, potholes, depressions, etc. Devices that can adapt to these situations do so in a mechanically undesirable manner which, among other things, places too much weight behind the rear axle of the towing vehicle.
Eighth, in order to lift the towed vehicle, some currently available wheel-lift devices tilt the wheel supports, so that the plane of the parallel members is not horizontal. The front parallel member supporting the lifted wheel may be at a lower height than the rear parallel member. This aggravates the tendency of the towed vehicle to roll out toward the towing vehicle. Even if the vehicle does not roll out, the vehicle body may be damaged because the rear parallel member is bulky in comparison to the small wheel-to-wheel well clearance in modern automobiles. It is especially desirable that any towing device not damage the body of the towed vehicle.